atan, atanf, atanl − arc tangent function
float atanf(float x);
long double atanl( long double x);
Link with −lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
These functions calculate the principal value of the arc tangent of x; that is the value whose tangent is x.
On success, these functions return the principal value of the arc tangent of x in radians; the return value is in the range [−pi/2, pi/2].
If x is a NaN, a NaN is returned.
If x is +0 (−0), +0 (−0) is returned.
If x is positive infinity (negative infinity), +pi/2 (−pi/2) is returned.
No errors occur.
For an explanation of the terms used in this section, see attributes(7).
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
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